A variable gain amplifier is used in, e.g., a mobile phone or a communication terminal which supports a wireless LAN (Local Area Network), and amplifies a signal level in wireless communication.
The variable gain amplifier can be classified into two types, i.e., an analog-control variable gain amplifier that controls the impedance thereof with an analog voltage, and a digital-control variable gain amplifier that controls the impedance thereof with a digital voltage. Compared to the analog-control variable gain amplifier, the digital-control variable gain amplifier eliminates the need for a digital-to-analog converter (DAC) and can reduce current consumption and footprint.
For example, a variable gain amplifier of Patent Literature 1 is known as prior art relating to the digital-control variable gain amplifier. The variable gain amplifier of Patent Literature 1 is a digital-control variable gain amplifier of the differential input type that amplifies a differential input signal and outputs the amplified signal as a differential output signal. In the variable gain amplifier of Patent Literature 1, a switch, a resistance, and a switch are cascade-connected in this order between the source terminals of the respective first and second transistors serving as a differential pair. In the variable gain amplifier of Patent Literature 1, ON and OFF of the two switches are controlled by digital signals serving as control signals, and thus the impedance between ground and the source of each of the first and second transistors changes so as to vary a gain.